Tuesday, August 28, 2012

A Math Problem Revisited

One of the advantages of teaching in a learning
center rather than a classroom is that I often get to see
the same student at various stages of his or her academic life. A
student who is in one of my precalc classes today was the very first
student I ever taught. Back then it was number facts and place value.
Today it's trig identities and parametric equations. While I haven't
seen this student every year since first grade, we've reunited for key
math events. We were together for whole number operations, met again for
fractions, and stayed close through algebra and geometry. The
opportunity to observe students over the entire length of their K-12
careers has been an incredible learning experience. It has given me a
unique perspective regarding how children learn math and how various
math programs succeed or fail in preparing students for each new stage
of concept development.

One of the math
classes I'm teaching combines problem solving with computer programming.
The group is made up of 8th graders I had taught a few years back. They
had participated in a math olympiad course. One type of problem that
appeared frequently dealt with simultaneous equations. For example,

At the movie theatre, tickets cost $6 for adults and $5 for children.A total of 24 people went to the movies and paid $128 for tickets.How many children went to the movies?

At
the elementary level, the students were encouraged to create a chart to
keep track of the number of adults and children, and total cost. The
process is simply an organized version of guess and check. The
efficiency of this method is dependent on the extent of number sense
developed by the students and the number of potential solutions.

I
thought it would be interesting to revisit this type of problem four
years later from a different angle. If we removed the constraint of the
total number of people, would we be able to find the exact number of
reasonable solutions to the problem? In this case, only positive integer
values would be sensible since the problem deals with whole people.

We
had done some hand graphing of linear equations, so I led the group in
that direction. The students identified the variables and came up with
an equation to graph, 6x + 5y = 128. They determined that there were 4
combinations of adults and children that would result in a total cost of
$128. The graph showed that while there were an infinite number of
solutions to the equation, only 4 solutions made sense in the context of
the problem.

We then talked about other
situations that would result in an equation of this type and developed
the general equation, ax + by = c. Next, I challenged them to create a
computer program that would find all positive, integer solutions of this
generalized equation. From the graph, the students knew that we needed
to test all x values from zero to some equation dependent maximum value.
The students were familiar with programming loops and agreed that this
would be the best approach. Here's the pseudo-code version of what the
group invented.

for(all values of x from 0 to nMax){y = (c-ax)/b; //rearranged equation in terms of yif(we divide y by 1 and get a remainder of zero){then y is an integerthis xy pair is a solutionstore these values}else{y is not an integerthis xy pair is not a solution}} So
far so good. My students were very proud that they were able to work
out the logic in this program. They had to figure out a way to calculate
the maximum value of x, determine if a number was an integer, and
decide what to do when y was an acceptable value. Each of these areas
led to rich discussions and deeper connections. Our next step is to find
a way to display our results in both graph and chart form.

If
I'm fortunate enough to teach these students a couple of years from
now, perhaps I could challenge them to develop an algorithm based on
parametric equations.

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About the Author

Colleen King is a math educator with 15 years experience working with K-12 students in a variety of settings. Colleen publishes MathPlayground.com and develops math games, teaching tools, and learning resources that are used in classrooms throughout the world. She has presented her work at ISTE and NCTM conferences and has co-authored several teaching articles.